Can dirty input power trip small thermal magnetic circuit breakers ? 3

[bdn2004]

A new rectifier system is installed on an existing unit substation as the simplified sketch shows below. The 45A thermal magnetic circuit breakers that feed the small rectifiers trip shortly after the system is powered up. They heat up to 150 degrees F per infrared testing. We measured the THD at the Mains as shown. The results show a total harmonic distortions at the connection point is 1% Voltage and 18% current.

The manufacturer of the rectifier equipment is claiming the 45A circuit breakers are tripping due to "dirty" input power and of no fault of their own. Note there are fairly large VFDS installed and HVAC equipment off the same substation bus. There are other small loads in the HVAC equipment that have operated for years without tripping. Is the manufacturer right ? Are there other things that could be causing this that we should check for?

 

[waross]

And by the way, in regards to dirty power:

The results show a total harmonic distortions at the connection point is 1% Voltage and 18% current.

The 18% current distortion is mostly due to the rectified equipment.
At your measuring point, the only current is feeding the filter and rectifiers.
The distortion caused by the rectifiers is probably responsible for part of the 1% voltage THD.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[TugboatEng]

If you stay on the tugboats long enough, you will eventually see a good example of a bad connection causing premature trips.

I have and it's usually burned contacts that cause the trouble which is why I brought up the interrupt rating earlier.

 

[davidbeach]

Sheesh, didn’t pay enough attention to what “dirty power” was. 1% voltage THD isn’t “dirty power” by any stretch of the imagination. Your current THD wants to create all the voltage THD it can but the source is so stiff that all you get is 1% VTHD? Problem lies elsewhere.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[jghrist]

Your power monitor is on the source side of the filter. What is the current distortion on the rectifier side of the filter?

 

[TugboatEng]

If you stay on the tugboats long enough, you will eventually see a good example of a bad connection causing premature trips.

On the boats it's almost always burned/worn contacts that are the source of the heating as the breakers are used as switches.

 

[Arentsch]

@che12345
"...The source can only supply distorted voltage and voltage alone doesn't heat anything. Distorted current flow does. If the 20A has a decent amount of higher frequency harmonics then it could be causing the breakers to heat up. 20A of 60hz should not".

@WAROSS
The 18% current distortion is mostly due to the rectified equipment.
At your measuring point, the only current is feeding the filter and rectifiers.
The distortion caused by the rectifiers is probably responsible for part of the 1% voltage THD.

This is the info I was trying to confirm. The plant's power system cannot provide the total harmonic current distortion. This is the rectifier manufacturer's problem not the plant's. Thank you.